Preparation of Sodium Ion Doped Copper Bismuth Oxide Photocathode and Its Photoelectrocatalytic Performance

Ternary oxide, as a class of photoelectrode materials, are considered promising for solar energy conversion. Copper bismuthate (CuBi₂O₄) photocathode is one of the ideal photocathode materials with great potential and application value in photoelectrochemical water splitting, however, its development and application still face great challenges due to its inherent problem of slow carrier mobility. In this study, CuBi₂O₄ photocathode was prepared by spray pyrolysis and the breakthrough of photoelectrochemical performance was realized by morphology modulation and defect regulation. Firstly, by doping Na⁺ into the CuBi₂O₄ photocathode (Na-CuBi₂O₄), the Bi³⁺ sites is replaced by the low-valence Na⁺ and hole centers are formed, thus enhancing the carrier transmission capacity. Meanwhile, the introduction of Na⁺ led to a porous nanomorphology of the prepared CuBi₂O₄ photocathode, which effectively shortened the transmission distance of photogenerated carriers to the surface. Secondly, by annealing Na-CuBi₂O₄ in oxygen atmosphere (Na-CuBi₂O₄-O₂), the Na-CuBi₂O₄-O₂ photoelectrode forms multiple metal vacancies as electron acceptors, which reduces the oxygen vacancies brought by Na⁺ doping, thus increasing the hole density and further improving the charge separation efficiency. This strategy resulted in a high photocurrent density of –2.83 mA·cm^–2 at 0.6 V vs. RHE for the Na-CuBi₂O₄-O₂ photoelectrode, which is 15 times higher than that of the untreated CuBi₂O₄ photoelectrode (–0.18 mA cm^–2). By combining time-resolved fluorescence spectroscopy, Kelvin probe force microscopy and photoelectrochemical studies, it was revealed that the Na-CuBi₂O₄-O₂ photoelectrode exhibits longer carrier lifetime and higher surface photovoltage. In a word, this work utilizes elemental doping and metal vacancies to enhance the charge separation and transfer ability of CuBi₂O₄ photocathode, realizing a significant improvement in its photoelectrochemical performance, which is of guiding significance for the future development of high-performance photocathodes.